This invention is directed to an improvement in a mechanical brake assembly and more specifically to an improved motion transmitting member for a brake assembly in which the brake shoes are moved by a floating actuating lever.
A balanced, two shoe internally expanding mechanical brake assembly actuated by a lever pivoting in a plane adjacent the brake shoe webs is disclosed in U.S. Pat. No. 2,852,105 issued to B. E. House et al. on Sept. 16, 1958. That brake assembly offers many advantages including the use of stamped steel brake drums, interchangeable brake shoes and springs, and relatively few moving parts which do not require lubrication. That brake assembly also does not require adjustment because the cam or ramp surfaces provided to the actuating lever body insure sufficient brake shoe movement for balanced braking action throughout the useful life of the brake shoe linings.
In that brake assembly, the braking force is applied to the brake shoes by motion transmitting members which include a boss at one end which is interposed between the actuating lever and a brake shoe. The other end of the motion transmitting member is pivotally mounted to the backing plate. The actuating lever is mounted for pivotal movement about an axis which is not fixed relative to the brake assembly while bearing against the bosses provided by each motion transmitting member. Since the motion transmitting members are pivotally mounted to the backing plate and the actuating lever is freely mounted between the brake shoes and the backing plate, the actuating lever is free to move relative to either brake shoe within the limits of other elements of the assembly. This free movement of the actuating lever between the brake shoes insures that the radial braking force developed by the cam surface or surfaces of the actuating lever will be equally applied to each of the brake shoes. The motion transmitting members thus serve to transmit movement of the actuating lever to the brake shoes and to equalize the radial force applied to each brake shoe. Since none of the elements of the brake assembly, except the abutments are fixed to the backing plate, relatively complex stress patterns may develop in certain elements of the assembly when the brake is actuated under an emergency stopping condition.
The motion transmitting members have traditionally been formed from cast peralitic malleable iron and finished to provide bearing surfaces where necessary in the brake assembly. Although cast iron motion transmitting members have proven satisfactory over many years of service it has recently been noted that such members are relatively brittle in comparison to other elements of the brake assembly which all formed from steel stock, and therefore, may be more likely to fail under emergency stopping conditions than the other elements in the assembly.
The present invention is concerned with this potential problem and provides an improved motion transmitting member for a mechanical brake assembly and a method of making the improved motion transmitting member.